This invention relates to a low pressure discharge lamp and particularly to a fluorescent low pressure discharge lamp.
In the known low pressure discharge lamps, the electron emissive electrodes that are employed have a coil structure in which the electron emissive material is provided as a coating on a coiled tungsten wire.
A problem with such an electrode is that it is difficult to provide an adequate control of the amount of emissive material provided on the coiled tungsten wire. As a result, it is very difficult to control the life distribution of the lamps so as to manufacture lamps having a narrowly controlled life distribution. This is because the lamp life is very sensitive to the quantity of emissive material provided on the electrode. Since it is almost impossible to uniformly control amounts of emissive material provided on a coated tungsten wire electrode it is difficult to manufacture lamps having an adequately narrow life distribution.
Another problem exists in that fact that due to the physical nature of the electrode employing a tungsten coil, it is impossible to fabricate the electrode into a particularly desired shape.
Further, fabricating an electrode in which the emissive material is loaded on to a double helix electrode, such as the ones presently employed, is a rather difficult operation and requires expensive equipment.